PTC device, protective circuit module including the same, and secondary battery including the protective circuit module

ABSTRACT

A Positive Temperature Coefficient (PTC) device, a Protective Circuit Module (PCM) including the PTC device, and a secondary battery including the Protective Circuit Module (PCM) are provided. A support portion is formed at one end of a conductive plate of the PTC device, a conductive layer disposed on the upper portion of the PTC main body is fixed to the Protective Circuit Module (PCM), and the support portion is fixed by a coated adhesive that is melted at a high temperature and then hardens when the high temperature is removed, thereby preventing the PTC device from swaying or twisting.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/145,819 titled “PTC DEVICE, PROTECTIVE CIRCUIT MODULE INCLUDING THESAME, AND SECONDARY BATTERY INCLUDING THE PROTECTIVE CIRCUIT MODULE”filed on Jun. 25, 2008, which claims the benefit of Korean ApplicationNo. 2007-113642, filed Nov. 8, 2007 in the Korean Intellectual PropertyOffice, the disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Aspects of the present invention relate to a secondary battery, and moreparticularly, to a Positive Temperature Coefficient (PTC) device, aProtective Circuit Module (PCM) including the PTC device, and asecondary battery including the Protective Circuit Module (PCM).

2. Description of the Related Art

Among the types of prismatic secondary batteries, a bare cell generallycomprises a can, electrode assemblies stored in the can, and a capassembly connected to the can. Safety devices such as PositiveTemperature Coefficient (PTC) devices and thermal fuses are installedoutside bare cells. Each safety device is connected to at least oneelectrode terminal of a bare cell and the device blocks current fromflowing outside the bare cell when the battery temperature rises, or thebattery voltage falls below or rises above a reference voltage becauseof excessive charge and discharge. PTC devices prevent batteries fromdamage and deterioration.

PTC devices have recently been installed in Protective Circuit Modules(PCM's). Solder based surface mount technologies can be used in order tomount the PTC device. For example, in a Protective Circuit Module (PCM)in which an electrical terminal having a conductive layer is exposed,the terminal of a PTC device is disposed on the electrical terminalhaving a conductive layer. The Protective Circuit Module (PCM) passesthrough a high temperature region. The conductive layer on the surfaceof the electrical terminal of the Protective Circuit Module (PCM) meltsand then hardens so that the terminal of the PTC device is bothelectrically connected to the electrical terminal of the ProtectiveCircuit Module (PCM) and is physically fixed thereto.

However, PTC devices are generally long with respect to the dimensionsof a bare cell or PCM and both ends thereof in the length direction areformed as terminals in order to connect a PTC device to bare cells orProtective Circuit Modules (PCM's). Since only one terminal is disposedon the conductive layer of the electrical terminal of anyone ProtectiveCircuit Module (PCM), the original directions in which PTC devices aredisposed may twist out of the designed orientation because of externalforces during the manufacturing process or when the conductive layermelts in the high temperature region. This causes a problem in weldingbare cells and the terminal as well as causes an external short-circuitsince a portion of the PTC devices goes beyond the range of thickness ofthe bare cells.

Conventional PTC devices are connected to Protective Circuit Modules(PCM's) by soldering on surface mount devices (SMDs) using a surfacemount technology (SMT). Although the SMT is used to mount PTC devices onSMDs by soldering, since one side of the PTC devices is fixed by asolder method but the other side thereof is not fixed by the soldermethod, PTC devices may sway or twist either during a mounting processor a subsequent process.

SUMMARY OF THE INVENTION

Aspects of the present invention provide a Positive TemperatureCoefficient (PTC) device that does not sway or twist when it is beingmounted on a Protective Circuit Module (PCM) or subsequently, theProtective Circuit Module (PCM) including the PTC device, and asecondary battery including the Protective Circuit Module (PCM).

Another aspect of the present invention provides a Positive TemperatureCoefficient (PTC) device comprising: a PTC main body; a conductive layercontacting the upper surface of the PTC main body; a conductive platecontacting the lower surface of the PTC main body; and a support portionformed in the conductive plate, wherein the support portion has the sameheight as the upper side of the conductive layer substantiallycorresponding to the height between the conductive plate and an edgethereof upward.

The support portion is formed by bending one end of the conductiveplate. The conductive plate comprises a lower end plate in which the PTCmain body is placed, a higher end plate in which the support portion isformed, and a connecting portion for connecting the lower end plate andthe higher end plate in a stepped manner. The conductive layer is aplate formed of nickel or nickel alloy.

Another aspect of the present invention provides a Protective CircuitModule (PCM) for a secondary battery comprising: a circuit board mainbody; a conductive pattern installed in the circuit board main body; anda PTC device comprising a PTC main body, a conductive layer contactingthe upper surface of the PTC main body and electrically connecting tothe conductive pattern, a conductive plate contacting the lower surfaceof the PTC main body, and a support portion formed as part of theconductive plate, wherein the support portion has the same height as theheight of the conductive layer substantially corresponding to the heightbetween the conductive plate and an edge thereof upward.

The conductive plate comprises a lower end plate in which the PTC mainbody is placed, a higher end plate in which the support portion isformed, and a connecting portion for connecting the lower end plate andthe higher end plate in a stepped manner. An adhesive is coated on thelower surface of the circuit board main body that contacts the supportportion. The adhesive may be a thermoplastic or thermosetting adhesive.A welding hole is formed in an area of the circuit board main body thatoverlaps the higher end plate.

The conductive layer of the PTC device in one aspect of the presentinvention constitutes a part of the PTC device and may be formed on thesurface of the electrical terminal. Thereafter, the conductive layer isplaced between the PTC main body and one electrical terminal of thewhole Protective Circuit Module (PCM), and all become one integralpiece.

Another aspect of the present invention provides a secondary batterycomprising: i) a bare cell; ii) a Protective Circuit Module (PCM)electrically connected to the bare cell, wherein the Protective CircuitModule (PCM) comprises: a circuit board main body and a conductivepattern installed in the circuit board main body; and iii) a PTC devicecomprising a PTC main body, a conductive layer contacting the uppersurface of the PTC main body and electrically connected to theconductive pattern, a conductive plate contacting the lower surface ofthe PTC main body, and a support portion formed in the conductive plate,wherein the support portion has the same height as the height of theconductive layer substantially corresponding to the height between theconductive plate and an edge thereof upward, and wherein one terminal ofthe bare cell is electrically connected to the conductive plate.

The one terminal of the bare cell is an electrode terminal, wherein awelding hole is formed in an area of the circuit board main body thatoverlaps the electrode terminal, and the electrode terminal and theconductive plate are combined in an area of the circuit board main bodythat overlaps the welding hole.

The conductive plate comprises a lower end plate in which the PTC mainbody is placed, a higher end plate in which the support portion isformed, and a connecting portion for connecting the lower end plate andthe higher end plate in a stepped manner. The electrode terminalprotrudes from the surface of the cap plate, the lower surface of thehigher end plate and the upper end of the electrode terminal contacteach other, and the step between the lower surface of the higher endplate and the lower surface of the lower end plate is smaller than theheight of the electrode terminal that protrudes from the cap plate. Anadhesive is coated on the lower surface of an insulating board thatcontacts the support portion.

Additional aspects and/or advantages of the invention will be set forthin part in the description which follows and, in part, will be obviousfrom the description, or may be learned by practice of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects and advantages of the invention will becomeapparent and more readily appreciated from the following description ofthe embodiments, taken in conjunction with the accompanying drawings ofwhich:

FIG. 1 is a perspective view of a Positive Temperature Coefficient (PTC)device according to an embodiment of the present invention;

FIG. 2 is a side-sectional view of a PTC device according to theembodiment of FIG. 1;

FIG. 3 is a perspective view of a PTC device according to anotherembodiment of FIG. 1;

FIG. 4 is a perspective view of a PTC device according to yet anotherembodiment of FIG. 1;

FIG. 5 is a cross-sectional view of a Protective Circuit Module (PCM)according to an embodiment of the present invention;

FIG. 6A is a bottom plan view of a Protective Circuit Module (PCM)according to the embodiment of FIG. 5;

FIG. 6B is a plan view of a Protective Circuit Module (PCM) according toanother embodiment of FIG. 5;

FIG. 7 is an exploded perspective view of a secondary battery accordingto an embodiment of the present invention; and

FIG. 8 is a front cross-sectional view of a secondary battery accordingto the embodiment of FIG. 7.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Reference will now be made in detail to the present embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings, wherein like reference numerals refer to the like elementsthroughout. The embodiments are described below in order to explain thepresent invention by referring to the figures. Moreover, it is to beunderstood that where it is stated herein that one layer is “formed on”or “disposed on” a second layer, the first layer may be formed ordisposed directly on the second layer or there may be an interveninglayer between the first layer and the second layer. Further, as usedherein, the term “formed on” is used with the same meaning as “locatedon” or “disposed on” and is not meant to be limiting regarding anyparticular fabrication process.

FIG. 1 is a perspective view of a Positive Temperature Coefficient (PTC)device 100 according to an embodiment of the present invention. FIG. 2is a side-sectional view of PTC device 100 according to the embodimentof FIG. 1. In FIGS. 1 and 2, PTC device 100 comprises a conductive plate101, a PTC main body 105 formed on the conductive plate 101, and asupport portion 107 formed at one end of the conductive plate 101.

The conductive plate 101 is formed of nickel and comprises a higher endplate 102, a lower end plate 103, and a connecting portion 104 forconnecting the higher end plate 102 and the lower end plate 103 in astepped manner. The higher end plate 102 is a conductive plate extendingfrom the upper end of the connecting portion 104 formed in a verticaldirection. The higher end plate 102 comprises the support portion 107that is formed by bending upward the end of the higher end plate 102that is opposite to the connecting portion 104. A recessed portion 108is formed in the plane of the higher end plate 102 and is spaced apartby a predetermined distance from the connecting portion 104 between theconnecting portion 104 and the support portion 107.

The lower end plate 103 is a conductive plate extending from the lowerend of the connecting portion 104 formed in a parallel plane to thehigher end plate 102 and extending away from the higher end plate 102and the support portion 107. The PTC main body 105 and a conductivelayer 106 formed on the upper surface of the PTC main body 105 areformed on the lower end plate 103. The height from the upper surface ofthe lower end plate 103 to the upper end of the support portion 107corresponds to that from the lower surface of the PTC main body 105 tothe upper surface of the conductive layer 106.

The connecting portion 104 connects the higher end plate 102 and thelower end plate 103 of the conductive plate 101 in a stepped manner sothat the support portion 107 formed on one end of the high end plate 102contacts a Protective Circuit Module (PCM) (see FIGS. 5 through 6B), andthe conductive layer 106 formed on the lower end plate 103 iselectrically connected to one end of the Protective Circuit Module(PCM).

The PTC main body 105 is disposed on the upper surface of the lower endplate 103. The conductive layer 106 is disposed on the PTC main body105, and is electrically connected to one terminal formed on theProtective Circuit Module (PCM). Soldering of the conductive layer 106to the Protective Circuit Module (PCM) will be described in detail inconnection with the Protective Circuit Module (PCM) later. Theconductive layer 106 may be one terminal 403 of the Protective CircuitModule (PCM) (see FIG. 5), preferably a plate formed of nickel or anickel alloy connected to an electrical terminal or the like.

The support portion 107 is formed by bending an end of the higher endplate 102 upward such that the support portion 102 contacts theProtective Circuit Module (PCM). If there is no support portion 107,when devices are being connected to the Protective Circuit Module (PCM)during the assembly of a secondary battery, or during a subsequentassembly process, the PTC device 100 sways or twists. Therefore, thesupport portion 107 is formed at one end of the higher end plate 102,and that one end of the higher end plate 102 otherwise disposed awayfrom the Protective Circuit Module (PCM) also contacts the ProtectiveCircuit Module (PCM). Now at least one surface of the Protective CircuitModule (PCM) and the support portion 107 contact each other and arejoined by an adhesive, thereby preventing the PTC device 100 fromswaying or twisting during the process of mounting the PCT device on thesurface of other devices or the process of assembling the secondarybattery.

The recessed portions 108 are formed at both sides of the higher endplate 102 in the plane of the higher end plate 102, are typicallysemi-circular shaped and are at locations adjacent to the connectingportion 104. The recessed portions 108 are used to place a repair toolwhen the PTC device 100 moves or is repaired, and allow the PTC device100 to be more easily mounted to the Protective Circuit Module (PCM)when the PTC device 100 moves or is repaired.

PTC devices according to other embodiments of the present invention willnow be described. FIG. 3 is a perspective view of a PTC device 200according to another embodiment of the invention of FIG. 1. Referring toFIG. 3, the support portion 207 of the PTC device 200 is different fromthe support portion 107 of the PTC device 100 shown in FIGS. 1 and 2. Inthe present embodiment, the support portion 207 will be described. Sameor similar portions as those of the embodiment of FIGS. 1 and 2 use thesame reference numerals and thus detailed descriptions thereof are notrepeated.

The support portion 207 is formed by bending an end of the higher endplate 102 upward. Grooves formed at a predetermined interval in themiddle of the support portion 207 form support portions 207 a and 207 bthat are separate from each other within the support 207. The supportportion 207 can perform the same function as the support portion 107that is formed in one piece. When the support portion 207 is fixed byapplying an adhesive to the lower portion of a Protective Circuit Module(PCM) (again see FIGS. 5 through 6B), even if one of the supportportions 207 a and 207 b is separated from the Protective Circuit Module(PCM), the support portion 207 can be more easily repaired since theother support portion remains fixed to the Protective Circuit Module(PCM).

FIG. 4 is a perspective view of a PTC device 300 according to yetanother embodiment of the invention of FIG. 1. Referring to FIG. 4, asupport portion 307 of the PTC device 300 is different from the supportportion 107 of the PTC device 100 shown in FIGS. 1 and 2. In the presentembodiment, the support portion 307 will be described. Same or similarportions as those of the embodiment of FIGS. 1 and 2 use the samereference numerals and thus detailed descriptions thereof are notrepeated.

The support portion 307 is formed by bending an end of the higher endplate 102 upward. The support portion 307 may be in the shape of aplurality of semicircles or other shapes. The plurality of semicircularsupport portions 307 can perform the same function as the supportportion 107 that is formed in one piece. When the support portion 307 isfixed by applying an adhesive to the lower portion of a ProtectiveCircuit Module (PCM) (again see FIGS. 5-6B), the plurality ofsemicircular surfaces of the support portion 307 are connected to theProtective Circuit Module (PCM), thereby reducing each area of thesupport portion 307 connected to the Protective Circuit Module (PCM) andthus loads on the Protective Circuit Module (PCM) can be reduced.

A Protective Circuit Module (PCM) including the PTC device according toan embodiment of the present invention will be described. FIG. 5 is across-sectional view of a Protective Circuit Module (PCM) 400 accordingto an embodiment of the present invention. FIG. 6A is a bottom plan viewof the Protective Circuit Module (PCM) according to the embodiment ofFIG. 5. Referring to FIGS. 5 and 6A, the Protective Circuit Module (PCM)400 comprises a circuit board main body 401, a conductive pattern 404installed on the circuit board main body 401, and the PTC device 100.

A welding hole 402 is formed in the middle of the circuit board mainbody 401. At least one electrical device 406 such as a necessary chip orresistance is mounted on the upper portion of the circuit board mainbody 401. A first terminal 403 and the conductive pattern 404 areinstalled at the lower portion of the circuit board main body 401.

The welding hole 402 is formed at an area of the Protective CircuitModule (PCM) 400 that overlaps the higher end plate 102 of the PTCdevice 100. In more detail, the welding hole 402 is formed at the areaoverlapping the high end plate 102 from a direction perpendicular to asurface of the Protective Circuit Module (PCM) 400. The reason for theformation of the welding hole 402 will be described with reference to asecondary battery according to another embodiment of the presentinvention (See FIGS. 7 and 8).

The first terminal 403 is disposed on the lower surface of theProtective Circuit Module (PCM) 400 and is an electrode terminal. Thefirst terminal 403 is electrically connected to the PTC device 100.

The conductive pattern 404 is formed on the circuit board main body 401.The conductive layer 106 formed on the upper portion of the PTC mainbody 105 and first terminal 403 are soldered to each other and thus thefirst terminal 403 and the PTC device 100 are electrically connected toeach other.

A thermoplastic adhesive is applied on an adhesive layer 409 at bothside ends of the Protective Circuit Module (PCM) 400 where the adhesivelayer 409 contacts the support portion 107 as well as at the surface ofthe Protective Circuit Module (PCM) 400 that does not contact thesupport portion 107. The thermoplastic or thermosetting adhesive is notapplied at a predetermined part in the middle of the adhesive layer 409.The conductive pattern 404 and the conductive layer 106 that aredisposed on the first terminal 403 installed in the Protective CircuitModule (PCM) 400 contact each other. The conductive pattern 404 ismelted by hot air or a heat lamp. Thereafter, when the high temperatureis removed, the conductive pattern 404 becomes solid and the firstterminal 403 and the conductive layer 106 are combined with each other,so that the PTC device 100 can be electrically and physically connectedto the PCM 400. The adhesive or the adhesive layer 409, which is appliedon the surface of the Protective Circuit Module (PCM) 400 and isinitially hard, is melted by hot air or heat. The melted adhesive layer409 that contacts the support portion 107 touching the ProtectiveCircuit Module (PCM) 400 hardens when the high temperature is removed,thereby fixing the support portion 107. Therefore, the higher end plate102 is fixed to the Protective Circuit Module (PCM) 400 and thus the PTCdevice 100 is unlikely to sway or twist. Although a thermoplastic(reversible) adhesive is described in the above embodiments, theadhesive layer 409 can be formed by laminating a thermosetting adhesiveusing various methods.

A Protective Circuit Module (PCM) including a PTC device according toanother embodiment of the present invention will now be described. FIG.6B is a plan view of a Protective Circuit Module (PCM) 500 according toanother embodiment of the invention of FIG. 5. The PTC device and thePCM of the present embodiment are different from the PTC devicedescribed with reference to FIGS. 1 to 4 and the PCM of FIGS. 5 and 6Aonly in terms of the adhesive layer 409 on which an adhesive foradhering the support portion 107 to the Protective Circuit Module (PCM)400 is applied. Therefore, in the present embodiment, only an adhesivelayer 509 that is disposed on the support portion 107 is described. Sameor similar portions as those of the embodiment of FIGS. 1 through 6A usethe same reference numerals and thus detailed descriptions thereof arenot repeated.

Referring to FIGS. 5 and 6B, the adhesive layer 509 is formed byapplying a thermoplastic adhesive on a portion of the Protective CircuitModule (PCM) 500 that contacts the support portion 107 and the othersurface of the Protective Circuit Module (PCM) 500 that does not contactthe support portion 107. The conductive pattern 404 and the conductivelayer 106 that are disposed on the first terminal 403 installed in theProtective Circuit Module (PCM) 400 contact each other. The conductivepattern 404 is melted by hot air or a heat lamp. Thereafter, when thehigh temperature is removed, the conductive pattern 404 becomes solidand the first terminal 403 and the conductive layer 106 are combinedwith each other, so that the PTC device 100 can be electrically andphysically connected to the PCM 500. The adhesive or the adhesive layer509, which is applied on the surface of the Protective Circuit Module(PCM) 500 and is initially hard, is melted by hot air or heat. Themelted adhesive layer 509 that contacts the support portion 107 touchingthe Protective Circuit Module (PCM) 500 hardens when the hightemperature is removed, thereby fixing the support portion 107.Therefore, the higher end plate 102 is fixed to the Protective CircuitModule (PCM) 500 and thus the PTC device 100 does not sway or twist.Compared to the PTC device 100 that is fixed to the Protective CircuitModule (PCM) 500 by applying the adhesive only on both ends of thesupport portion 107 (FIG. 6A), the PTC device 100 of FIG. 6B is morestably fixed to the Protective Circuit Module (PCM) 200 by applying theadhesive entirely on the support portion 107 and thus is unlikely tosway or twist. As with the previous embodiment, although a thermoplastic(reversible) adhesive is described in the above embodiments, theadhesive layer 509 can be formed by laminating a thermosetting adhesiveusing various methods.

A secondary battery including a Protective Circuit Module (PCM)according to an embodiment of the present invention will be describedwith reference to FIGS. 7 and 8. FIG. 7 is an exploded perspective viewof a secondary battery according to an embodiment of the presentinvention. FIG. 8 is a front cross-sectional view of a secondary batteryaccording to the embodiment of FIG. 7.

Referring to FIGS. 7 and 8, the secondary battery 600 comprises a barecell 10, a cap assembly 20 electrically connected to the bare cell 10,the PTC device 100 connected to an electrode terminal 23 included in thecap assembly 20, and the Protective Circuit Module (PCM) 400electrically connected to the PTC device 100.

The bare cell 10 comprises a can 11, an electrode assembly 12 stored inthe can 11, a positive electrode 13, a separator 14 and a negativeelectrode 15 forming the electrode assembly 12, a positive tab 16electrically connected to and extending from the positive electrode 13,a negative tab 17 electrically connected to and extending from thenegative electrode 15, and insulating tape 18 for preventing thepositive electrode 13 and the negative electrode 15 from beingshort-circuited.

The can 11 is a metal container formed with a prismatic shape and openat one end, and is formed using a processing method such as deep drawingor the like. Therefore, the can 11 can function as a terminal. The can11 may be formed of conductive aluminum or aluminum alloy. The can 11 isa container for the electrode assembly 12 and electrolyte. The openingof the can 11 for putting in the electrode assembly 12 is sealed by thecap assembly 20.

In the electrode assembly 12 the positive electrode 13 and the negativeelectrode 15 are formed in wide plates in order to increase electricalcapacity, the separator 14 is then laminated between the positiveelectrode 13 and the negative electrode 15 to insulate both electrodes,and the electrode assembly 12 is formed in a coil to form a shape like ajelly roll. The positive electrode 13 and the negative electrode 15 canbe formed respectively by coating two collectors each formed of aluminumfoil and copper with lithium cobalt oxide that is a positive electrodeactive material and carbon that is a negative electrode active material.

The separator 14 is formed of polyethylene, polypropylene, a co-polymerof polyethylene and polypropylene, or other similar polymers. It isadvantageous that the separator 14 is wider than the positive electrode13 and the negative electrode 15 in order to prevent the electrodeplates from short-circuiting. The positive tab 16 and the negative tab17 that are connected to each electrode are electrically connected tothe positive electrode 13 and negative electrode 15 respectively andextend from the electrode assembly 12. An insulating tape 18 is woundaround the boundary portion of the electrode assembly 12 from which thepositive tab 16 and the negative tab 17 extend in order to prevent theelectrode plates of the positive electrode 13 and the negative electrode15 from short-circuiting.

The cap assembly 20 comprises a cap plate 21, a gasket 22, an electrodeterminal 23, an insulating plate 24, a terminal plate 25, an insulatingcase 27, and a plug 26. The cap plate 21 is formed to include a terminalport hole 21 a and an electrolyte injection hole 21 b. When theelectrode terminal 23 is inserted into the cap plate 21, in order toinsulate the electrode terminal 23 and the cap plate 21, the circulargasket 22 for storing the electrode terminal 23 is placed on theexterior surface of the electrode terminal 23 through the terminal porthole 21 a. The electrolyte injection hole 21 b is formed at one end ofthe cap plate 21 to inject electrolyte into the can 11, and is sealedwith the plug 26 after electrolyte is injected into the can 11.

The insulating plate 24 is disposed at the lower surface of the capplate 21. The terminal plate 25 is installed at the lower surface of theinsulating plate 24. The insulating plate 24 insulates the cap plate 21and the terminal plate 25. The terminal plate 25 is connected to thelower portion of the electrode terminal 23. The negative electrode 15 ofthe electrode assembly 12 is electrically connected to the electrodeterminal 23 via the negative tab 17 and the terminal plate 25. Thepositive electrode 13 of the electrode assembly 12 with the positive tab16 is welded to the cap plate 21 or the can 11.

The insulating case 27 may be further disposed in the lower portion ofthe terminal plate 25. The insulating case 27 comprises a negative tabperforation portion 27 a, a positive tab perforation portion 27 c, andan electrolyte injection hole 27 b. In another embodiment, the positionsof the positive electrode 13 and the negative electrode 15 may bereversed.

The plug 26 is used to seal the electrolyte injection hole 21 b formedin the cap plate 21 after injecting electrolyte through the electrolyteinjection hole 21. Instead of the plug 26, a ball or other device can beused to seal the electrolyte injection hole 21 b after being pressedinto place.

In this way, a prismatic bare cell battery is completely formed. Theprismatic bare cell battery is connected to the Protective CircuitModule (PCM) 400 so that the electrode terminal 23 of the prismatic barecell battery can contact the higher end plate 102 of the PTC device 100shown in FIG. 5 or FIGS. 6A and 6B.

The lower surface of the higher end plate 102 of the PTC device 100 isconnected to the electrode terminal 23 of the bare cell battery. The PTCmain body 105 is formed on the upper surface of the lower end plate 103of the PTC device 100 and the conductive layer 106 is formed on theupper portion of the PTC main body 105 so that the conductive layer 106is combined with the first terminal of the Protective Circuit Module(PCM) 400. The connection between the higher end plate 102 of the PTCdevice 100 and the electrode terminal 23 of the bare cell battery ismade by welding. The welding is made by flowing current through thecontact surface between the higher end plate 102 and the electrodeterminal 23 of the bare cell battery and forming a welding portion at apart of the contact surface by using a resistance welding bar downwardvia the welding hole 402 formed on the circuit board main body 401. Theconductive layer 106 and the first terminal of the Protective CircuitModule (PCM) 400 are combined with each other after the conductivepattern installed on the circuit board main body 401 is melted at a hightemperature and hardens when the high temperature is removed.

The cap plate 21 serves as another electrode terminal of the bare cellbattery. Each of connection leads 405 fixed to both lower ends of thecircuit board main body 401 is connected to both ends of the cap plate21 in the length direction. At least one of the connection leads 405 isconnected to a second terminal of the lower surface of the circuit boardmain body 401, so that the cap plate 21 is electrically connected to thesecond terminal of the lower surface of the circuit board main body 401.Thus, the Protective Circuit Module (PCM) 400 is electrically connectedto the bare cell.

The PTC device 100 is placed in the current circulation path between theProtective Circuit Module (PCM) 400 and the bare cell to operate when itreceives heat coming from the bare cell battery or outside, and blockscurrent flow to prevent a safety accident such as an explosion orignition of a battery or the like.

According to aspects of the present invention, a support portion isformed at an end of a conductive plate section of a PTC device and isfixed to a Protective Circuit Module (PCM) when a conductive layerdisposed on the upper layer of the PTC device is surface mounted. Thisprevents a defective connection to an electrical terminal or a shortcircuit from outside due to a PTC device that may have moved or twisted.

The support portion is more easily fixed to the Protective CircuitModule (PCM) by using an adhesive that has been previously coated on theProtective Circuit Module (PCM), thereby preventing the PTC device fromswaying or twisting.

Although a few embodiments of the present invention have been shown anddescribed, it would be appreciated by those skilled in the art thatchanges may be made in this embodiment without departing from theprinciples and spirit of the invention, the scope of which is defined inthe claims and their equivalents.

What is claimed is:
 1. A secondary battery, comprising: an electrodeassembly; a can for accommodating the electrode assembly; and aProtective Circuit Module (PCM) electrically connected to the electrodeassembly, wherein the PCM comprises: a circuit board main body, and apositive temperature coefficient (PTC) device interposed between thecircuit board main body and the electrode assembly, the PTC deviceelectrically connected to the circuit board main body, wherein the PTCdevice comprises two end portions and a middle portion between the twoend portions, the two end portions contact the circuit board main bodyand the middle portion is spaced apart from the circuit board main body.2. The secondary battery of claim 1, wherein the circuit board main bodyhas a welding hole spaced apart from the PTC device when the electrodeassembly is inserted into the PCM.
 3. The secondary battery of claim 1,wherein the PTC device comprises a PTC main body, and the PTC main bodyis coupled with the circuit board main body.
 4. The secondary battery ofclaim 3, wherein the PTC device further comprises: a conductive layercontacting an upper surface of the PTC main body; a conductive platecontacting a lower surface of the PTC main body; and a support portionformed in the conductive plate.
 5. The secondary battery of claim 4,wherein the support portion has substantially the same height as theheight of the conductive layer, wherein the height of the conductivelayer substantially corresponds to the height between the conductiveplate and an edge thereof upward.
 6. The secondary battery of claim 4,wherein the support portion is formed by bending one end of theconductive plate.
 7. The secondary battery of claim 4, wherein theconductive layer is formed of nickel or a nickel alloy.
 8. The secondarybattery of claim 4, wherein the conductive plate comprises a lower endplate in which the PTC main body is placed, a higher end plate in whichthe support portion is formed, and a connecting portion connecting thelower end plate and the higher end plate in a stepped manner.
 9. Thesecondary battery of claim 8, wherein an adhesive is coated on the lowersurface of the circuit board main body that contacts the supportportion.
 10. The secondary battery of claim 9, wherein the adhesive is athermoplastic or thermosetting adhesive.
 11. A secondary battery,comprising: an electrode assembly; a protective Circuit Module (PCM)comprising a circuit board main body and a positive temperaturecoefficient (PTC) device; the PTC device comprising: a support portion;a plate; and a body portion electrically connected to the electrodeassembly; the support portion having a first end contacting the circuitboard main body and a second end integrated to the plate, the platehaving a gap to the circuit board main body, and the body portiondisposed on the plate and electrically connected to the circuit boardmain body.
 12. The secondary battery of claim 11, wherein the platecomprises at least one step.
 13. The secondary battery of claim 12,wherein the plate comprises a first plate portion, and a second plateportion.
 14. The secondary battery of claim 13, wherein the first plateportion and the second plate portion are connected to one another in astepped manner.
 15. The secondary battery of claim 11 further comprisinga can to house the electrode assembly.
 16. The secondary battery ofclaim 11 further comprising a cap assembly, wherein the PTC device isinterposed between the cap assembly and the PCM circuit main body. 17.The secondary battery of claim 16 further comprising a first electrodetab and a second electrode tab interposed between the plate and the capassembly.
 18. The secondary battery of claim 17, wherein the first andsecond electrode tabs are electrically connected to the plate.